April 4, 2009, marks the sixtieth anniversary of the signing of the North Atlantic Treaty. The grand alliance that toppled Napoleon lasted less than a decade; the alliance that defeated Hitler crumbled in fewer than five years. Why has the Atlantic Alliance lasted so long? Why this alliance and not others?

I said in the Preface that I would use this book to develop two themes. The first is that NATO, for various reasons, became something very different than the military alliances formed by the great powers prior to the Second World War – so different that it does not fit well in an all-inclusive category labeled “alliances.” The second is that NATO, as an alliance of democracies, possesses hidden strengths that have enabled it to overcome – not just once but again and again – the kind of internal disputes that destroyed virtually all previous and many contemporary alliances. Taken together, these two themes suggest that an alliance of liberal democracies should exhibit behaviors very different from those found in alliances with only one or no democracies.

In the rest of this chapter, I revisit these two themes in order to highlight the new knowledge about alliances in general and NATO in particular that this approach makes possible.

WHY NATO IS DIFFERENT

Alliances are among the oldest and most enduring phenomena of international relations, but the reasons why they form, their intended duration, and their organizational structure have changed greatly over the past several centuries.